Various types of aquarium aerators are known in the prior art. However, what has been needed is an aeration fitting for an aquarium including a hollow outer fitting having an interior channel, a cylindrical back portion, a cylindrical front portion having a threaded outer surface, a tapered cylindrical middle portion, and a frontwardly flared outer lip. A floating ball is disposed within the interior channel of the outer fitting. What has been further needed is a hollow inner fitting having an inner channel, a cylindrical posterior portion, a cylindrical anterior portion having a threaded inner surface, a tapered cylindrical central portion, and a frontwardly flared inner lip. A spring is disposed within the inner channel of the inner fitting. Lastly, what has been needed is for each of the back portion of the outer fitting and the posterior portion of the inner fitting to be connectable to an air hose, and for the threaded outer surface of the front portion to be selectively engageable with the threaded inner surface of the anterior portion within an aperture in a wall of an aquarium. The aeration fitting for an aquarium thus helps to protect an air hose from being disturbed and displaced by fish swimming in the aquarium, since it can be hid from view and run under the gravel layer at the bottom of the aquarium. The hiding of the air hose at the bottom of the aquarium not only helps to decrease the maintenance needed on the aquarium, but also results in a more visually pleasing aquarium by eliminating the need to run an air hose from the top of the aquarium into the water.